Without milk production, offspring cannot survive, making MCL-1 essential for survival of mammalian species, the researchers discovered. Professors Nai Yang Fu, Geoff Lindeman and Jane Visvader from the Walter and Eliza Hall Institute in Australia led the research published on Tuesday in the journal Nature Cell Biology.

Visvader said MCL-1 was found to be an important regulator of breast development and its milk-producing cells.

"This study has unlocked one of the key survival factors in the mammary gland," Visvader said in a statement.

"MCL-1 is important for all stages of breast development, from puberty to pregnancy and lactation. Based on this discovery, it is reasonable to believe that every mammal requires MCL-1 for milk production and, ultimately, the survival of their offspring."Fu said .

"We were able to use very sensitive technologies to determine that stem cells and luminal cells were the breast cells that most critically rely on MCL-1," Fu added."

Luminal cells are the cells that line breast ducts and respond to hormones during puberty, pregnancy and lactation. It now seems clear that MCL-1 is integral to the survival of these cells," Visvader said, adding that the discovery further underscored the importance of MCL-1 for cell survival.

In addition to our discovery, a number of recent research studies at our institute have shown that MCL-1 is important for the survival of certain immune cells, and for the survival and growth of cancers including leukaemia and lymphoma," she said.

"Stem cells and luminal progenitor cells both require MCL-1 for their survival. Our team has previously implicated both these cell types in some types of breast cancer, raising the question of whether MCL-1 is an important target for developing anti-cancer drugs."

Lindeman, Visvader and their breast cancer research team have spent the past 15 years unravelling the secrets of normal breast development in a bid to improve our understanding, and ultimately treatment, of breast cancer.

"This is an exciting time for our research team. Some of the discoveries we have made on breast development and how it goes awry in cancer have helped to identify potential targets for therapy, leading to preclinical studies and clinical trials aimed at breast cancer treatment or prevention."